1. Field of the Invention
The present invention relates to Wideband Code Division Multiple Access of the 3G communication system, especially to a method for providing notifications for a Multi-media Broadcast/Multicast service.
2. Description of the Related Art
The Multimedia Broadcast/Multicast Service (hereinafter referred to as MBMS) is a new service under standardization by 3G Mobile Communication System Partnership Project (hereinafter referred to as 3GPP). The service provided in virtue of broadcast or multicast is an unidirectional point-to-multipoint (i.e. multimedia data sent from a single data source are transferred to multiple users through network transmission) service. The most remarkable feature of the service is that it can make use of radio resources and network resources efficiently. MBMS service is mainly used in wireless communication network system, e.g. Wideband Code-Division Multiple Access system, Global System of Mobile Communication, etc. MBMS service data transfer basically includes following several steps, i.e. data source transmission, middle network transmission, destination cell on-the-air transmission and user receiving. As shown in FIG. 1, Broadcast and Multicast Service Center 70 (hereinafter referred to as BM-SC) is the data source for MBMS data transmission; Gateway GPRS Supporting Node 60 (hereinafter referred to as GGSN) is used to connect GRPS network with external network, such as INTERNET; In MBMS service, the Gateway GPRS Supporting Node connects to the BM-SC and sends MBMS data to specific Service GPRS Supporting Node 50 (hereinafter referred to as SGSN); SGSN is used to perform access control on UE as well as mobility management, and sends MBMS data from GGSN to specific Radio Network Controller 30 (hereinafter referred to as RNC) at the same time; RNC is used to control a group of base stations like station 23 and 24 and sends multimedia data to specific base stations like station 23 and 24; a base station 23 establishes air common channel 11 for MBMS service of cell 21 under the control of the RNC; a base station 24 establishes air common channel 12 for MBMS service of cell 22 under the control of the RNC; Terminal User Equipment 10 (hereinafter referred to as UE) is a terminal equipment for MBMS data reception.
FIG. 4 shows a whole process from service announcement, joining of a user, service notification, establishment of radio bearer to leaving of the user finally in MBMS service.
401 Subscription: Establish a connection between a user and a service provider, and authorize the user to receive a relevant MBMS service.
402 Service Announcement: Notify a user of services that will be provided. For example, the system will rebroadcast a football match in Beijing at 7:00 p.m.
403 Joining: Refers to that the user joins a group, i.e. the user informs the network that he or she is willing to receive this multicast service.
404 MBMS Session Start: Refers to establish a network resource for MBMS data transfer.
405 MBMS Notification: Notify the user of MBMS data transfer that will be performed right away.
406 Data transmission: Refers to the process of transferring MBMS service data to the user.
407 MBMS Session Stop: Refers to release the network resource after the MBMS service data transfer process is completed.
408 leaving: Oppositely to 403 joining, which indicates that the user is leaving the group, i.e. the user doesn't want to receive the data of a certain service any more.
Because step 405 is the content that the present invention should emphasize, it will be introduced in detail in the following. FIG. 2 is referred for more information. There are many conditions to activate the RNC to perform MBMS notifications, for instance, to inform the UE that the MBMS session starts, to re-count the number of users, to inform the UE that the session is completed, etc. Two steps are applied to carry out the MBMS notification: first, an indication bit is set for each corresponding MBMS service which needs to send notifications in a cell's Multi-media Broadcast/Multicast Indication Channel (hereinafter referred to as MICH) (202), and the UE receives the MICH via the air interface (203); next, the corresponding RRC messages are transferred through the Multi-media Broadcast/Multicast Control Channel (hereinafter referred to as MCCH), indicating the actions of the UE (204). The structure of the MICH is shown in FIG. 5. In the MICH, 300 bits are available in use, and in general, only the fore 288 bits are used, leaving alone the rest 12 bits. The actual number of MICH bits used in the service is not involved in the present invention. Here, let N be the number of available bits in an MICH frame, these N bits are divided into Np groups with each group indicating only one MBMS service group within a frame, and the number of bits needed for a group is just N/Np.
A time when the UE tunes in the MICH corresponds to its own user ID, and the tuning in locations each time it wakes up are different to every frame. In the MBMS, in order to carry out the MBMS notification for all UEs that have subscribed this service, all UEs should be enabled to detect that the notification indication bit NI of the MICH has been set to true for the subscribed service, thus repeating to send said service notification within a certain period, which is defined as the modification period, as shown in FIG. 3.
Since the MICH has limitation in information transfer, it exists such moment that different services map to the same location of the MICH. To reduce this probability, a method for spreading NI is proposed in the WCDMA system so that each service's corresponding location NI in a frame is made different from any others with a certain algorithm. In this way, the probability that several services correspond to the same location NI can be reduced so as to avoid that the notification NI received by the UE is not the very one for the service that the UE has subscribed.
According to this method, the data sent to the Node B in each frame is needed to be calculated by the RNC and transferred to the Node B through FP. Usually, if indicator of a certain service is true, then the specific N/Np bits in the MICH must be set as true within the whole modification period. This means that the RNC should send data to the Node B in every frame, thus, the traffic through an interface lub becomes comparatively larger and higher requirements are put forward to the needed transmission equipments. If this condition could be improved, not only the traffic through the interface lub can be reduced, but also the operating efficiency of the Node B can be enhanced. By the existing technique, the contents to be transferred through the MICH are well calculated by the RNC according to some algorithm based on mapping relationship, and generally, the RNC transfers the Np bits to the Node B through the frame protocol FP in the interface lub, with each bit indicating whether the corresponding service is true or false. Then, the Node B maps each bit to the N/Np bits of the MICH and transmits it to the UE via the air interface.